• Bulletin of the Korean Chemical Society
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• v.33 no.6
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• pp.1993-1997
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• 2012

Mg-doped ZnO one-dimensional (1D) nanostrutures were synthesized by using a thermal evaporation technique. The morphology, crystal structure, and sensing properties of the Mg-doped ZnO nanostructures functionalized with Pt to CO gas at $100^{\circ}C$ were examined. The diameters of the 1D nanostructures ranged from 80 to 120 nm and that the lengths were up to a few tens of micrometers. The gas sensors fabricated from multiple networked Mg-doped ZnO nanowires functionalized with Pt showed enhanced electrical response to CO gas. The responses of the nanowires were improved by approximately 70, 69, 111, and 81 times at CO concentrations of 10, 25, 50, and 100 ppm, respectively. Both the response and recovery times of the nanowire sensor for CO gas sensing were not nearly changed by Pt functionalization. It also appeared that the Mg doping concentration did not influence the sensing properties of ZnO nanowires as strongly as Pt-functionalization. In addition, the mechanism for the enhancement in the CO gas sensing properties of Mg-doped ZnO nanowires by Pt functionalization is discussed.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.213-213
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• 2010

Magnetic random access memory (MRAM), based on magnetic tunnel junction (MTJ) and CMOS, is one of the best semiconductor memories because it can provide nonvolatility, fast access time, unlimited read/write endurance, low operating voltage and high storage density. For the realization of high density MRAM, the etching of MTJ stack with good properties is one of a key process. Recently, there has been great interest in the MTJ stack using MgO as barrier layer for its huge room temperature MR ratio. The use of MgO barrier layer will undoubtedly accelerate the development of MTJ stack for MRAM. In this study, high-density plasma reactive ion etching of MgO films was investigated in an inductively coupled plasma of $Cl_2$/Ar gas mixes. The etch rate, etch selectivity and etch profile of this magnetic film were examined on vary gas concentration. As the $Cl_2$ gas concentration increased, the etch rate of MgO monotonously decreased and etch slop was slanted. The effective of etch parameters including coil rf power, dc-bais voltage, and gas pressure on the etch profile of MgO thin film was explored, At high coil rf power, high dc-bais voltage, low gas pressure, the etching of MgO displayed better etch profiles. Finally, the clean and vertical etch sidewall of MgO films was achieved using $Cl_2$/Ar plasma at the optimized etch conditions.

• Korean Journal of Medicinal Crop Science
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• v.9 no.1
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• pp.26-32
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• 2001

The contents of chemical components such as total nitrogen, total amino acid and vitamin C were somewhat higher in $N_2$ gas treatment at $10^{\circ}C$ for 3 hours than those of other treatments. However, the contents of tannin and chlorophyll were slightly lower than that in the other treatments. The content of ${\gamma}-Aminobutyric$ acid with $N_2$ gas treatment was higher $1.5{\sim}6$ times with values of $51{\sim}205mg/100g$ than in control (35mg/100g). The scores of sensory test was not different between $N_2$ gas treatment for 3 hours and control. The contents of chemical components such as total nitrogen, total amino acid including theanine and caffeine were slightly higher in $N_2$ gas treatment at $20^{\circ}C$ for 3 hours than those of other treatments. However, the contents of tannin and vitamin C were slightly lower than those of other treatment. The content of GABA in tea leaves treated with $N_2$ gas was higher $2.5{\sim}7$ times with values of $85{\sim}225mg/100g$ than in control (35mg/100g). The sensory test was lower in $N_2$ gas treatment($76.3{\sim}78.1$ point) than in control(80.4 point). The contents of chemical components were not different between $N_2$ gas treatment at $30^{\circ}C$ for 3 hours and control. Whereas the contents of chemical components were somewhat lower in $N_2$ gas treatment for 1 hour and 5 hours than in control. The content of GABA in tea leaves treated with $N_2$ gas was higher $3{\sim}7$ times with values of $115{\sim}217mg/100g $than in control(35mg/100g). The sensory test was lower in $N_2$ gas treatment ($74.3{\sim}78.4$ point) than in control(80.4 point). Consequently, tea mading within 5 time $N_2$ gas treatment at $10^{\circ}C$ or 3 time $N_2$ gas treatment at 20, $30^{\circ}C$ after plucking was considered to be the best green tea in terms of functional nature as well as taste nature.

• Journal of Powder Materials
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• v.16 no.4
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• pp.275-279
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• 2009

The aging characteristics of gas atomized Mg-6 wt.% Al-1 wt.% Zn alloy were investigated and compared to those of cast Mg-6 wt.% Al alloy. The gas atomized Mg-6 wt.% Al-1wt.% Zn alloy powders had spherical morphology between 1 and 100 $\mu m$ in diameter. After compaction under the pressure of 700 MPa at $320^{\circ}C$ for 10 min, the Mg-6 wt.% Al-1 wt.% Zn alloy showed a grain size of approximately 40 $\mu m$ which is smaller than that of the cast Mg-6 wt.% Al alloy, and a relative compact density of approximately 93%. After ageing, the Mg-6 wt.% Al-1 wt.% Zn alloy showed much faster peak hardness than cast Mg-6 wt.% Al alloy. The Mg-6 wt.% Al-1 wt.% Zn alloy showed the new fine precipitations with ageing time, while the cast Mg-6 wt.% Al alloy was almost similar morphology.

• Journal of Korea Foundry Society
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• v.30 no.6
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• pp.224-230
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• 2010

To prevent oxidation of Mg melt, $SF_6$ gas has been generally used for Mg alloys during melting and casting as a cover gas. The use of $SF_6$ gas, however, will be restricted owing to its crucial impact on global warming. Non-$SF_6$ process during melting and casting in diecasting industry has been proved with Eco-Mg alloys by a simple addition of small amount of CaO into Mg alloys. This paper shows non-$SF_6$ diecasting procedures for 0.7wt% CaO added AZ91D Eco-Mg alloys. Cold-chamber diecasting was performed under $CO_2$ atmosphere without $SF_6$ gas. An increment of mechanical properties, especially strength and ductility of Eco-Mg alloys is, in part, due to high-quality melt, refined grain size and $Al_2Ca$ second phase strengthening. Microstructures and mechanical properties of 0.7wt% CaO added AZ91D Eco-Mg alloys are evaluated in comparison with those of conventional AZ91D Mg alloy.

• Journal of Sensor Science and Technology
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• v.31 no.6
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• pp.455-460
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• 2022

Brush-like ZnO hierarchical nanostructures decorated with MgxZn1-xO (x = 0.1, 0.2, 0.3, 0.4, and 0.5) were fabricated and examined for application to a gas sensor. They were synthesized using vapor phase growth (VPG) on indium tin oxide (ITO) substrates. To generate electronic accumulation at ZnO surface, MgZnO nanoparticles were prepared by sol-gel method, and the ratio of Mg and Zn was adjusted to optimize the device for NO₂ gas detection. As the electrons in the accumulation layer generated by the heterojunction reacted faster and more frequently with the gas, the sensitivity and speed improved. When tested as sensing materials for gas sensors at 100 ppm NO₂ at 300℃, these MgZnO decorated ZnO nanostructures exhibited an improvement from 165 to 514 times compared to pristine ZnO. The response and recovery time of the MgZnO decorated ZnO samples were shorter than those of the pristine ZnO. Various analyzing techniques, including field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray powder diffraction (XRD) were employed to confirm the growth morphology, atomic composition, and crystalline information of the samples, respectively.

• Carbon letters
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• v.13 no.4
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• pp.254-259
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• 2012

Nanoporous non-woven carbon fibers for a gas sensor were prepared from a pitch/polyacrylonitrile (PAN) mixed solution through an electrospinning process and their gas-sensing properties were investigated. In order to create nanoscale pores, magnesium oxide (MgO) powders were added as a pore-forming agent during the mixing of these carbon precursors. The prepared nanoporous carbon fibers derived from the MgO pore-forming agent were characterized by scanning electron microscopy (SEM), $N_2$-adsorption isotherms, and a gas-sensing analysis. The SEM images showed that the MgO powders affected the viscosity of the pitch/PAN solution, which led to the production of beaded fibers. The specific surface area of carbon fibers increased from 2.0 to $763.2m^2/g$ when using this method. The template method therefore improved the porous structure, which allows for more efficient gas adsorption. The sensing ability and the response time for the NO gas adsorption were improved by the increased surface area and micropore fraction. In conclusion, the carbon fibers with high micropore fractions created through the use of MgO as a pore-forming agent exhibited improved NO gas sensitivity.

• Journal of Korea Foundry Society
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• v.9 no.6
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• pp.474-482
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• 1989

The aim of this research is to investigate the effects of gas bubbles on the formation of spheroidal graphite in cast iron, Fe-Si-8%Mg alloy, mischmetal hydride($MmH_2$) and $CaCO_3$, which discharge various amounts of Mg, $H_2$ and $Co_2$, gases, were added to Fe-3.9% C-2.0%Si melt and the melt was innoculated with 0.3wt% of 75%Fe-Si. The spheroidal graphites and/or compacted vermicular graphites were produced with more than 0.625cc/g of Mg gas or more than 0.3125cc/g of $H_2$ gas while $CO_2$ gas did not contribute to graphite spheroidization. Nodule counts increased with the amount of Fe-Si-Mg added ; but they decreased with the amount of $MmH_2$ added because the number of effective gas bubbles decrease with the increase in Mm residual. The bull's eye structure was revealed with 0.625cc/g, 1.25cc/g of Mg and 0.3125cc/g of $H_2$ ; the ledeburite structure was revealed with more than 0.625cc/g of $H_2$.

• Journal of Powder Materials
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• v.14 no.2 s.61
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• pp.140-144
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• 2007

Using Spark Plasma Sintering process (SPS), consolidation behavior of gas atomized $Mg_{97}Zn_1Y_2$ alloys were investigated via examining the microstructure and evaluating the mechanical properties. In the atomized ahoy powders, fine $Mg_{12}YZn$ particles were homogeneously distributed in the ${\alpha}-Mg$ matrix. The phase distribution was maintained even after SPS at 723 K, although $Mg_{24}Y_5$ particles were newly precipitated by consolidating at 748 K. The density of the consolidated bulk Mg-Zn-Y alloy was $1.86g/cm^3$. The ultimate tensile strength (UTS) and elongation were varied with the consolidation temperature.

• Journal of Powder Materials
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• v.14 no.6
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• pp.372-379
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• 2007

The microstructure, mechanical and electrochemical properties of plasma electrolytic coatings (PEO) coatings on Mg-4.3 wt%Zn-1.0 wt%Y and Mg-1.0 wt%Zn-2.0 wt%Y alloys prepared by gas atomization, followed by compaction at 320 for 10 min under the pressure of 700 MPa and sintering at 380 and 420 respectively for 24 h, were investigated, which was compared with the cast Mg-1.0 wt%Zn alloy. All coatings consisting of MgO and $Mg_2SiO_4$ oxides showed porous and coarse surface features with some volcano top-like pores distributed disorderly and cracks between pores. In particular, the surface of coatings on Mg-1.0 wt%Zn-2.0 wt%Y alloy showed smaller area of pores and cracks compared to the Mg-4.3 wt%Zn-1.0 wt%Y and Mg-1.0 wt%Zn alloys. The cross section micro-hardness of coatings on the gas atomized Mg-Zn-Y alloys was higher than that on the cast Mg-1.0 wt%Zn alloy. Additionally, the coated Mg-1.0 wt%Zn-2.0 wt%Y alloy exhibited the best corrosion resistance in 3.5%NaCl solution. It could be concluded that the addition of Y has a beneficial effect on the formation of protective and hard coatings on Mg alloys by plasma electrolytic oxidation treatment.